Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $56.84   6.137%   $60.3283   $60.33   $60.35   $60.30  
  Purchase #2 $183.78   6.482%   $195.6926   $195.69   $195.70   $195.70  
  Purchase #3 $73.33   4.530%   $76.6518   $76.65   $76.65   $76.70  
  Purchase #4 $48.25   11.180%   $53.6444   $53.64   $53.65   $53.60  
  Purchase #5 $154.79   10.640%   $171.2597   $171.26   $171.25   $171.30  
  Purchase #6 $90.92   11.246%   $101.1449   $101.14   $101.15   $101.10  
  Purchase #7 $170.91   8.830%   $186.0014   $186.00   $186.00   $186.00  
  7 purchase totals = $778.82       $844.7231   $844.71   $844.75   $844.70